What is it?

This summer's fitness fashion statement, the FitFlop, is supposedly a thigh-toning sandal that has gathered a cultish following among wearers convinced it gives them longer, leaner legs.

How do they work?

According to the makers, the "mid-step is designed to tone thighs, activate muscles and tone the calves and gluteal muscles", as well as reduce joint strain by "recreating the gait of barefoot walking". The rounded sole creates instability so that your leg, buttock and core muscles are purportedly engaged with every step.

Looks familiar ...

These are very different to the MBT (Masai Barefoot Technology) trainers, claim the Fitflops designers, biomechanists Dr David Cook and Darren James of the Human Performance Centre at London's South Bank University. They have flatter soles, are more lightweight and shock-absorbing and have a patent pending for the design.

Anything else?

FitFlops can be worn every day, but in short bursts only. Unlike normal shoes, they will not rub and are therefore said to be good for bunion sufferers. However, although designed by academics, there are no published scientific studies confirming the benefits.

Where can I get them?

At the moment only women's styles and sizes are available (£36 a pair) but a men's range will come next year. For stockists, see thefitflop.com.

Expert's verdict

"I am concerned that people think you can put them on and turn into Cameron Diaz," says Trevor Lewis, a consultant physiotherapist specialising in feet and lower limbs at Knowsley Primary Healthcare Trust in Merseyside. "I'm not sure these would get you any fitter than ordinary walking."